1. Field of the Invention
The present invention relates to a fusing unit of an electrophotographic image forming apparatus, and more particularly, to a sheet separating apparatus for a fusing unit which is to separate a sheet of paper being conveyed through a fusing unit from a heating roller and guides the sheet to a discharging roller.
2. Description of the Related Art
An electrophotographic image forming apparatus transfers an image formed on a photosensitive medium to a sheet of printing paper and fuses the transferred image onto the sheet by using heat and pressure from a fusing unit. The fusing unit has a heating roller generating heat and a pressing roller applying pressure to the sheet, both of which are rotatably disposed opposing each other. The transferred image is fused onto the sheet while passing between the heating roller and the pressing roller. After that, the image-fused sheet is discharged out of the image forming apparatus by a discharging roller.
However, when the image is fused onto the sheet passing through the fusing unit, the sheet is inclined to roll toward the heating roller by the influence of the heated toner that is used to form the transferred image. Accordingly, there is a concern that the fused sheet may not be discharged out of the image forming apparatus by the discharging roller and instead may become jammed between the heating roller and the frame.
In order to prevent this problem, a sheet separating apparatus for a fusing unit is required, which separates a sheet being conveyed through the fusing unit and rolled toward the heating roller from the heating roller and conveys the sheet to the discharging roller. FIG. 1 shows an example of a fusing unit of an electrophotographic image forming apparatus employing such a sheet separating apparatus.
Referring to FIG. 1, a fusing unit includes a frame 11, a sheet guide 13, a heating roller 15, a pressing roller 16, and a sheet separating apparatus 30.
The sheet guide 13 guides a sheet of printing paper 10 being conveyed from a developing unit (not shown) with an image being transferred to an upside surface of the sheet 10 between the pressing roller 16 and the heating roller 15.
The heating roller 15 is rotatably disposed in the frame 11, generates the heat necessary to fuse the transferred image onto the sheet 10 and also supports the sheet 10 as it is pressed by the pressing roller 16. The pressing roller 16, which is used to fuse the transferred image onto the sheet 10 together with the heating roller 15, is disposed in the frame 11 to press the sheet 10 against the heating roller 15 with a predetermined constant pressure.
The sheet separating unit 30 includes a separating claw 31 and a contact spring 36. The separating claw 31 is disposed toward a paper discharging side of the heating roller 15 to separate the sheet conveyed through the fusing unit 12 from the heating roller 15. At this time, the separating claw 31 is pivotably assembled with a hinge 34 secured to the frame 11 and has a front end 32 constantly in contact with a surface of the heating roller 15. At this point, the front end 32 is sharpened as much as possible so as not to form a gap between the front end 32 and the contacting surface of the heating roller 15 (see FIG. 2). Also, the separating claw 31 has to be made of a synthetic resin or other suitable material having a heat resisting property since it is constantly in contact with the heating roller 15 which is at a high temperature. The contact spring 36 presses the separating claw 31 so that the front end 32 of the separating claw 31 is constantly in contact with the surface of the heating roller 15. One end of the contact spring 36 is secured to the frame 11 and the other end is connected to the other end 35 of the separating claw 31. Accordingly, the separating claw 31 is pivoted on the hinge 34 toward the heating roller 15 so that the front end 32 of the separating claw 32 keeps pressing the surface of the heating roller 15 with a predetermined constant pressure.
A sheet discharging guide 20 is disposed in the frame 11 between a pair of discharging rollers 22, 23 and the heating roller 15, for guiding the sheet 10 separated by the sheet separating apparatus 30 to the pair of discharging rollers 22, 23.
Hereinafter, operation of the conventional sheet separating unit for the fusing unit will be described.
The sheet 10 being conveyed from the developing unit (not shown) with the image transferred thereto is guided by the sheet guide 13 and enters into the space between the heating roller 15 and the pressing roller 16. As the sheet 10 passes between the heating roller 15 and the pressing roller 16, the transferred image is fused onto the sheet 10. The sheet 10 passes between the heating roller 15 and the pressing roller 16, and rolls up along the heating roller 15 due to the characteristics of the toner used to form the image and the heat applied thereto. A front periphery of the sheet 10 being conveyed along the heating roller 15 is separated from the heating roller 15 by the front end 32 of the separating claw 31 and is conveyed along the sheet discharging guide 20. The printing sheet 10 being conveyed along the sheet discharging guide 20 is discharged out of the image forming apparatus by the pair of discharging rollers 22, 23. That is, the sheet 10 passing between the heating roller 15 and the pressing roller 16 and stuck to the heating roller 15 is separated from the heating roller 15 by the sheet separating apparatus 30 and discharged out of the image forming apparatus by the pair of the discharging rollers 22, 23.
However, when the sheet separating apparatus 30 is installed, or when a sheet of paper 10 is jammed between the separating claw 31 and the heating roller 15 and removed, it is often the case that corners of the sharpened front end 32 of the separating claw 31 cause damage to the surface of the heating roller 15.
Also, it is required to sharpen the front end 32 of the separating claw 31 as much as possible, but the method for fabricating the separating claw 31 by injection-molding of the synthetic resin makes it difficult to sufficiently sharpen the front end 32 of the separating claw 31. Accordingly, in order to solve this problem, a method has been suggested that is to separately fabricate the front end 32 and attach the front end to the separating claw 31. In that case, however, there is a problem of increased fabrication cost.
Accordingly, there is a recognized need to develop a sheet separating device for a fusing unit capable of preventing damage to the heating roller and a method of easily fabricating the sharpened front end, thereby preventing fabrication costs from being increased.